Copolyester-carbonates and the methods for preparing them are well-known in the prior art. Products made from copolyester-carbonates exhibit such properties as high impact strength, toughness, high transparency, wide temperature stability limits, good dimensional stability, good creep resistance and the like. Copolyester-carbonates can be formed into articles of various shapes including thin films. It is also desirable to provide copolyester-carbonates having improved flame-retardance so that thin films and other products made from such copolyester-carbonates, can be safely used by the consumer and also meet the increasing requirements of certain flame retardant criteria being established by local and federal government agencies as well as the manufacturers of such products.
Among the copolyester-carbonates and the methods for preparing them which are well-known in the prior art, are those disclosed in U.S. Pat. Nos. 3,030,331; 3,169,121; and 3,207,814. U.S. Pat. No. 4,189,549 discloses polyester-carbonate copolymer compositions which are obtained from a melt polymerization process employing para-hydroxy benzoic acid. U.S. Pat. No. 4,156,069 discloses a process for preparing an alternating ester-carbonate block copolymer from dihydric phenols, dicarboxylic acid, dihalides, phosgene and a molecular weight regulator in the presence of pyridine. A typical copolyester-carbonate obtained therein consists of bisphenol-A, terephthalate and carbonate moieties having mole ratios from 2:0.8:1.2 to 2:1.3:0.7.
In U.S. Pat. No. 3,388,097, 4,4'-(1,1,1-trifluoroethylidene)diphenol was made from trifluoroacetaldehyde hydrate and phenol in the presence of anhydrous hydrogen fluoride in a pressure bomb. The product was distilled under reduced pressure at 165.degree.-170.degree. C. and 0.5-0.6 mm. Hg. Polyesters are made from these perhaloalkyl bisphenols and specified aromatic acid halides. However, it is noted that the acid catalyst is pressurized anhydrous hydrogen fluoride, and that the reaction product had to be distilled at 165.degree.-170.degree. C. at reduced pressure. The bisphenols which are useful in the preparation of the polyesters in U.S. Pat. No. 3,388,097 have the structure: EQU HO-Ar.sub.1 -Z-Ar.sub.1 -OH (1)
wherein Ar.sub.1 is para-phenylene, and Z is a divalent radical having the formula: ##STR1## wherein R and R' may be the same or different and represent perhalogenated lower alkyl groups, fluorine and chlorine being the preferred halogen species, with the provision that R' may represent hydrogen when R represents a perfluorinated lower alkyl group. These bisphenols are prepared under pressure by the acid catalyzed condensation of an appropriate halogenated ketone or aldehyde with two molecules of an appropriate phenol. However, there is no suggestion of high molecular weight polyester-carbonates or of the possibility of flame retardance of certain polyester-carbonates derived from fluorinated diphenols.
In U.S. Pat. No. 4,220,583, flame retardancy of polycarbonate compositions was improved by admixing a halogen-free aromatic polycarbonate and minor amounts of partially fluorinated polyolefin and minor amounts of an organic alkali metal salt or an organic alkaline earth salt, or mixtures thereof. Although these polycarbonate compositions containing flame retardant organic salts exhibit good flame retardancy, it is always desirable to achieve flame retardancy without resorting to additives.
In general, the prior art references recognize that flame retardance can be imparted to polycarbonates by chlorinating or brominating the monomeric building blocks from which they are obtained. None of these references, however, discloses or suggests that a high molecular weight polyester-carbonate copolymer composition having improved flame retardance can be obtained from the fluorinated diphenols.